Practise defining and calculating magnetic flux and flux linkage, explaining induction experiments, and applying Faraday’s and Lenz’s laws to induced e.m.f. and direction.
Define magnetic flux.
A square coil of wire of side length 12 cm consists of 8 insulated turns. The coil is stationary in a uniform magnetic field. The plane of the coil is perpendicular to the magnetic field, as shown in Fig. 6.1.
Fig. 6.1
The flux density B of the magnetic field varies with time t as shown in Fig. 6.2.
Fig. 6.2
Determine the magnetic flux linkage inside the coil at time . Give a unit with your answer.
State how Fig. 6.2 shows that the electromotive force (e.m.f.) E induced across the terminals between t=0 and is constant.
Calculate the magnitude of E.
The procedure in (b) is repeated, but this time the terminals of the coil are connected together.
State and explain the effect on the coil of connecting the terminals together during the change of magnetic flux density shown in Fig. 6.2.
A small solenoid of area of cross section is placed inside a larger solenoid of area of cross-section , as shown in Fig. 6.1.
Fig. 6.1 (not to scale)
The larger solenoid has 600 turns and is attached to a d.c. power supply to create a magnetic field.
The smaller solenoid has 3000 turns.
Compare the magnetic flux in the two solenoids.
Compare the magnetic flux linkage in the two solenoids.
State Lenz's law of electromagnetic induction.
The terminals of the smaller solenoid are connected together. The smaller solenoid is then removed from inside the larger solenoid.
With reference to magnetic fields, explain why a force is needed to remove the smaller solenoid.